The present invention relates to rotary mechanical seals used to prevent leakage of fluids along a shaft rotatable in a housing. Such seals utilize a pair of contacting washers: one annular washer or ring is sealed with respect to the shaft and rotates with the shaft; the other is sealed with respect to a housing and is stationary. The device of the present invention provides an improved drive to the rotatable washer to insure that the washer rotates with the rotation of the shaft.
Rotary mechanical seals are known and are particularly useful in a variety of applications, for example, in coolant pumps in the cooling systems of internal combustion engines. In such seals, one of the sealing washers is typically made of a hard, rigid material such as ceramic. In this application, the coolant may be subject to sudden and extreme temperature changes which subject the ceramic washer to thermal shock; the washer may expand unevenly, causing it to crack and the seal to fail.
To solve the thermal shock problem, U.S. Pat. No. 3,782,735, to Novosad, discloses the use of a metal band around the ceramic washer. The metal band has an interference fit with the ceramic washer at one end. At its opposite end, the band defines a radially directed annular fin. Because of the interference fit between the ceramic washer and the metal band, the ceramic washer is in a constant state of compression, thereby increasing the washer's resistance to thermal shock. The annular fin aids in dissipating heat from the ceramic washer into the fluid being pumped.
In the arrangement disclosed in Novosad U.S. Pat. No. 3,782,735 the ceramic washer is carried by a sleeve pressed onto the shaft. An elastomeric washer is disposed between the sleeve and the washer to provide a static seal and also to provide a means for driving the washer. While the rotary mechanical seal disclosed in Novosad U.S. Pat. No. 3,782,735, protects the ceramic washer from thermal shock, ceramic washers driven solely by this frictional connection between the washer and sleeve may, in some instances, spin relative to the pump shaft. To insure against this possibility, the present invention provides a rotary mechanical seal which uses an improved drive to rotate the ceramic washer.